The purpose of this study is to determine whether the likelihood of death in people with weak hearts can be lessened. There are two principal causes of death in people with decreased heart strength: progressive, profound heart muscle weakness and severe heart rhythm disorders (ventricular fibrillation). Ventricular fibrillation is a rapid disorganized beating of the lower heart chambers, (ventricles), causing death because the heart can no longer pump blood effectively. This study will examine whether ventricular fibrillation can be prevented. People with decreased heart strength can also die from progressive heart weakness. Entry into the study will not alter the standard care given to individuals for the treatment of a weak heart. Standard therapy includes the use of diuretics (water pills like furosemide and hydrochlorothiazide), afterload reducers (enalapril, lisinopril, captopril, hydralazine, nitrates, and related drugs) and/or, digitalis (digoxin). Standard therapy may also include blood thinners (aspirin and warfarin), beta-blockers (metoprolol, atenolol), and, in patients with severely weakened hearts, heart transplantation.